Optically addressable, integrative composite polymer microcapsules

Abstract

The development of remotely addressable tools to encapsulate, store and deliver active materials to living cells is a particularly challenging topic of material science. As drug delivery agents, microcontainers not only require high mechanical stability or to be delivered at target cells, but they should also possess efficient remotely addressable release mechanisms. Light responsive polyelectrolyte capsules are well suited for such purposes. Capsules are constructed using the Layer‐by‐Layer technique where oppositely charged polymers are alternatively deposited on a sacrificial template. The interest for such microcapsules lays in their versatile composition and stimuli‐responsive properties, which can be altered to suit specific needs. The primary aim of this work was to develop polymeric capsules with efficient optically addressable release mechanisms. Previous work on this topic revealed severe flaws in biological environments, especially with regards to the high energy requirements necessary for laser‐induced release and in the very limited knowledge of the fate of microcapsules in living cells. These issues were addressed by developing alternative types of light‐responsive capsules and gaining better understanding of existing ones. Three types of materials were used to sensitize microcapsules to the near‐UV, visible and near‐IR spectral regions: (1) azobenzene‐substituted polymers, (2) gold nanoparticles and (3) photocatalytic porphyrinoid dyes. Various methods were used for the characterization of microcapsules, including laser scanning confocal microscopy, colloidal probe and standard atomic force microscopy, electron microscopy, fluorescence spectrophotometry, UV‐visible spectroscopy and differential scanning calorimetry. Shells were probed for their mechanical stability as well as encapsulation and release behavior based on parameters such as: assembly strategies, shell deformability, permeability, thermal response and response to laser irradiation. This thesis begins with a brief introduction followed by an extensive literature review summarizing the various topics relevant to the work. The materials and methods used in the investigations are catalogued in Chapter 3 . Chapter 4 presents the destructive effects of pulsed UV lasing on polymeric microcapsules and introduces azobenzene‐functionalized capsules with the ability to encapsulate macromolecules by exposure to continuous wave UV light. Chapter 5 looks at the mechanical properties of capsules functionalized with gold nanoparticles as well as their remote release capabilities under near‐IR irradiation. While most of these studies were conducted ex vivo, Chapter 5 concludes with a summary of studies performed in vitro, which demonstrates that it is not only possible to release substances in living cells by light but that the latter also survive in the process. Finally, in Chapter 6, the assembly and light induced destabilization of microcapsules containing porphyrinoid dyes is presented.